TRENTON, N.J. — High-profile Republicans were adamant Sunday that Governor Chris Christie should not resign from his post as chairman of the Republican Governors Association after a recent assertion by a former ally that there is evidence Christie knew about an apparently politically motivated traffic jam earlier than he has said.

The support came from former mayor Rudy Giuliani of New York, Governor Bobby Jindal of Louisiana, and US Representative Paul Ryan of Wisconsin.

John Wisniewski, the Democratic chairman of a legislative committee investigating the September lane closures near the George Washington Bridge, was among those taking heat from Republicans who spoke out about the issue Sunday.

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Christie, a potential 2016 presidential contender, has been going about Super Bowl ceremonial duties — New Jersey was the host of Sunday’s championship game — and has not taken questions about the scandal in recent days.

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Christina Genovese Renna, a member of Christie’s administration who has been subpoenaed in an alleged political payback investigation, resigned Friday, she confirmed Sunday. Renna reported to Deputy Chief of Staff Bridget Kelly, who apparently set the lane closings in motion.

Giuliani, appearing on CBS’s ‘‘Face the Nation,’’ took aim at the credibility of Wisniewski and another figure central to the scandal — David Wildstein, the former Christie loyalist who as an executive at the Port Authority of New York and New Jersey last year ordered the lane closures.

On Friday, Wildstein’s lawyer wrote a letter to the Port Authority saying evidence exists that Christie knew about the traffic jams in Fort Lee as they happened. But he did not disclose any evidence in the letter.